The present disclosure relates generally to cellular telephone communications. More particularly, the present disclosure relates to overload coordination for cellular telephone intercell interference.
In the uplink of a cellular telephone system, cellular telephones within a cellular telephone cell transmit wireless cellular telephone signals to the base station serving the cell. However, the base station serving a cell receives wireless cellular telephone signals not only from cellular telephones within the cell, but also from cellular telephones in neighboring cells. The signals received from neighboring cells appear as interference, referred to as “intercell interference,” which severely limits the coverage and throughput of a network. FIG. 1 shows an example of intercell interference.
Referring to FIG. 1, a cellular telephone 108 located in one cell 104B transmits wireless cellular telephone signals 106, which are received by the base station 102B serving that cell 104B. However, wireless cellular telephone signals 106 are also received by a base station 102A serving a neighboring cell 104A. Signals 106 constitute intercell interference for base station 102A.
One way to mitigate intercell interference is to force neighboring cells to use different sections of the frequency spectrum. Although this helps to alleviate intercell interference, another problem remains that cannot be addressed by simple frequency domain separation. When cellular telephones at the edge of a cell transmit wireless cellular telephone signals at high power, they can cause the signal level received at a base station in a neighboring cell to be extremely high. This can cause the analog front end of the neighboring base station to be overloaded, leading to degradation of signal quality and loss of service in the neighboring cell.
One way to mitigate this type of base station overload is to use an overload indicator. FIG. 2 shows an example of the conventional use of an overload indicator to mitigate intercell interference. Referring to FIG. 2, when base station 102A becomes overloaded, base station 102A transmits overload indicators 110B-G to all neighboring base stations, including base station 102B. In response, the neighboring base stations instruct the cellular telephones within their cells to reduce transmit power. For example, base station 102B transmits an instruction 112 to all cellular telephones 108 in cell 104B. In response to instruction 112, cellular telephones 108 reduce their transmit power, thereby reducing intercell interference received by base station 102A.
One disadvantage of the conventional overload indicator approach is that a base station does not determine which cell is responsible for causing the intercell interference, and so sends the overload indicator indiscriminately to all neighboring cells. Therefore, even cells that are not causing significant intercell interference are forced to reduce their transmit power unnecessarily, leading to a decrease in throughput in those cells while providing no benefit to the overloaded cell.